Hydraulic cements are cements that set and develop compressive strength due to a hydration reaction, and thus can be set under water. As such, hydraulic cements are often used for cementing pipes or casings within a well bore of a subterranean formation for the construction of oil, gas and water wells, as well as other purposes, such as squeeze cementing. In the oil and gas industry, successful cementing of well pipe and casing during oil and gas well completion requires cement slurries having several important properties. The cement slurry must have a pumpable viscosity, fluid loss control, minimized settling of particles and the ability to set within a practical time.
In a typical completion operation, the cement slurry is pumped down the inside of the pipe or casing and back up the outside of the pipe or casing through the annular space. This seals the subterranean zones in the formation and supports the casing. Conventional mixing equipment for such applications is relatively complex and expensive. The equipment must wet dry cement powder, homogenize the mix, measure its density and, if necessary, recirculate it, such that additional solids or mixwater can be added to achieve the desired density. These varied requirements dictate the equipment's configuration and complexity.
Bulk equipment is usually pressurized so that solids can be transferred pneumatically at the relatively high rates required. Once at the drilling site, the pneumatically conveyed cementing solids must be correctly proportioned and mixed with the water, as well as other additives to form a pumpable slurry. The slurry must then be tested for the appropriate density, with the density adjusted to fall within the appropriate range. If cementing solids are not correctly proportioned, the quality of the cement diminishes.
U.S. Pat. Nos. 5,447,197 and 5,547,506 disclose storable cementitious slurries that remain liquid over an extended period of time and which can be activated at the time of use to meet specific job requirements. Such slurries contain, in addition to the cementitious slurry, a set retarder and a suspending agent. In U.S. Pat. No. 6,173,778 a carrageenan suspending agent is employed to provide a slurry under conditions of high pH and calcium ion content. Such cementitious slurries offer several advantages over the conventional cementing slurries of the prior art. Most notably, they be made in advance and stored until needed, thereby allowing the production of such slurries regardless if drilling has commenced. In addition, the storable cement slurry may be made at a different location from the job site. This storable slurry can then be transported to the job site before cementing. Further, the slurry can be stored in nonpressurized tanks and easily transferred. Still further, the mixing equipment used on the job site need only homogenize the slurry with any additional water and additives as required en route to the down hole pumps; activators may be added, mix water proportioned and additives introduced on-site to control the slurry's properties. Such storable slurries can further undergo quality control prior to introduction into the well. In addition, the need for sophisticated density control equipment is eliminated, thereby reducing the capital investment requirement for cementing equipment.
Unfortunately, such storable slurries are often difficult to apply universally due to variable cement quality, the need to use good quality mixwater and the lack of suitable quality control methodology to track the evolution of the slurry versus time after preparation. Such obstacles require great care and attention to detail. Storable slurries, which provide an easily measurable parameter, which accurately predicts the evolution of the storable slurry and its propensity to set, are therefore desired. In addition, it is desired that such cementitious slurries provide suspension stability and less tendency to exhibit particle sedimentation than the slurries of the prior art.